Electrical systems, power supply apparatuses, and power supply operational methods are described. According to one aspect, an electrical system includes an electrical entity configured to utilize electrical energy, and wherein the electrical entity comprises a communications interface, and a power supply apparatus configured to provide the electrical energy for use by the electrical entity, and wherein the power supply apparatus comprises a support system, a plurality of battery assemblies configured to be removably coupled with and supported by the support system, wherein individual ones of the battery assemblies comprise at least one rechargeable electrochemical device configured to provide the electrical energy, at least one power terminal configured to couple with the electrical entity and to provide the electrical energy from the electrochemical device to the electrical entity, and a communications interface configured to implement communications with the communications interface of the electrical entity, and wherein the electrical entity and the power supply apparatus are configured to implement the communications comprising at least one of status information regarding the power supply apparatus from the power supply apparatus to the electrical entity and a command regarding an operation of the power supply apparatus from the electrical entity to the power supply apparatus.